In the aircraft industry, there is a need for a lightweight portable drill that is capable of drilling holes in limited access areas, is capable of drilling holes in a variety of materials, and is economical to manufacture, use, and maintain. An example of a situation in which such a drill is needed is the installation of titanium bathtub fittings or seal pans. Such a fitting is illustrated in FIG. 2. The fitting acts as a fuel dam between wet and dry areas of a fuel tank. The fitting is attached to the skin of the tank and its integral stringers, as shown in FIG. 2. Fastener holes must be drilled from the inside of the fitting outward to avoid damage to the composite material skin. Thus, the drill must be capable of operating within the limited area inside the fitting. The type of fitting shown in FIG. 2 typically has dimensions of 2 inches.times.4 inches.times.2 inches. In addition, in some cases the fitting is not quite rectangular but has up to a 15.degree. slope to compensate for wing curvature. A survey of commercially available drills failed to uncover a drill suitable for use in the type of environment illustrated in FIG. 2.
The patent literature includes numerous examples of drills with widely varying characteristics. U.S. Pat. No. 3,679,320, granted July 25, 1972, to L. Bohorquez et al. discloses a portable pneumatic drill that is described as being designed for drilling holes in recessed areas where access is difficult. The drill has a body with a right angle motor at one end and a drill spindle at the opposite end. The motor drives the spindle by means of a gear train including meshing bevel gears. Two lead screws are positioned between the motor and the spindle. The screws are attached to a footplate which is adapted to be clamped to the underside of a workpiece, such as by a C-clamp. A second gear train drives the lead screws. One of the lead screws has adjustable stops to limit relative travel between the body and the footplate. The stops operate a limit valve. A pneumatically operated piston and cylinder activates a ball and detent clutch to engage and disengage the gear trains.
U.S. Pats. No. 3,804,544, granted Apr. 16, 1974, and No. 3,897,166, granted July 29, 1975, to R. D. Adams, issued on applications that were related as parent and divisional applications. These patents disclose a positive feed drill in which the motor drive shaft is concentric with the drill spindle. A parallel lead screw is engaged by a pivotable arm to move the drill housing relative to a pressure foot. The lead screw is driven by the motor via a gear train and is provided with a friction clutch. The pressure foot is connected to the housing by a guide shaft to which the arm is pivoted. A load on the pressure foot created by urging it against the workpiece activates the clutch. In one embodiment, a spring biased return shaft is provided for automatically advancing the pressure foot when pressure against the workpiece is removed. In two other embodiments, the housing is secured to a drilling fixture, or the pressure foot is clamped to the workpiece by a pin that threadedly engages the workpiece, and a cylinder urges the housing and pressure foot against the workpiece.
U.S. Pat. No. 2,961,899, granted Nov. 29, 1960, to J. E. Grove et al., discloses a drilling machine in which the spindle housing and driving mechanism is mounted on a frame for sliding to various elevations above a work support table. The drill spindle is parallel to the drive shaft of the motor and is driven thereby by means of a belt and pulley mechanism. A rack and pinion is manually operated to provide axial translation of the drill. The rack is in the form of a reciprocable screw positioned parallel to the spindle.
A positive feed drill having a coaxial drill spindle and lead screw and a parallel offset motor is disclosed in U.S. Pat. Nos. 434,576, granted Aug. 19, 1890, to H. B. Wyman; 2,791,922, granted May 14, 1957, to C. L. Robinson; 3,013,285, granted Dec. 19, 1961, to C. G. Arengo; 3,124,817, granted Mar. 17, 1964, to K. C. Mosier; and 4,182,588, granted Jan. 8, 1980, to R. C. Burkart et al. The Wyman drill includes lugs for attaching a clamp. The Robinson device has a manual dog-type clutch. The Arengo drill has a rod that is parallel to the drive shaft of the spindle and that moves with such drive shaft and carries stop nuts which engage switches to limit movement of the spindle. The Mosier device includes a dog-type clutch. One embodiment is described as being for use in remote, hard-to-reach locations and has a laterally elongated housing in which the drill spindle and drive shaft are mounted on opposite end portions. The Burkart et al. drill includes a dog-type, piston operated clutch and an annular nozzle on the nose surrounding the drill bit for cooling. One embodiment includes a sensing rod parallel to the spindle that engages the nose and is slidably supported in guide bushings.
U.S. Pat. Nos. 3,512,434, granted May 19, 1970, to D. P. Juhasz et al., and 4,083,646, granted Apr. 11, 1978, to P. G. Vindez, each disclose a positive feed drill with a lead screw coaxial with the drill spindle and an offset right angle motor. Juhasz et al. state that coolant may be provided through the spindle and that various fixtures and clamping devices may be used to secure the drill and workpiece together. The dog-clutch may be operated by a lever or a fluid operated piston. The drill spindle is provided with stop nuts for controlling limits of travel. The Vindez drill includes two piston valves for operating the clutches.
U.S. Pat. No. 3,429,206, granted Feb. 25, 1969, to R. C. Quackenbush, discloses a right angle positive feed drill with a unitary feed screw and spindle and a worm gear drive mechanism. U.S. Pat. No. 3,421,392, granted Jan. 14, 1969, to K. R. Bangerter et al., discloses a portable gun-type pneumatic hand drill in which a valve is actuated by contact with a workpiece to supply coolant fluid through a bore in the barrel of the bit. U.S. Pat. No. 4,097,175, granted June 27, 1978, to Y. Tsukiji, disclose as a combined drilling and turning machine in which a workpiece is mounted on a turntable and a pivotable bit is provided for drilling holes in right angular surfaces.
The above-cited patents and the prior art that is discussed and/or cited therein should be studied for the purpose of putting the present invention into proper perspective relative to the prior art.